During use, railroad wheels are subjected to high, long-term stresses. Despite being made of high-quality steel, the stresses cause the wheels to become worn over a long period of operation. Without maintenance, a wheel can become too thin or otherwise no longer of the correct geometry. Further, the wheels may develop other defects, such as, for example, a “slid flat” or “flat spot”, which is caused by locking the wheels with the brakes in an attempt to stop.
The wheels of railroad cars and locomotives cannot turn differentially since they are affixed to solid axles. As a result, any difference between the shape and/or size of the wheels on either side of a car/locomotive can cause a tendency to turn, leading to an increased possibility of derailment. Therefore, it is important to periodically inspect the wheels on railroad cars and locomotives to ensure that they remain safe to operate, both as an individual wheel and as a pair of wheels on the same axle.
The use of a J-shaped, steel wheel gauge is a common approach to inspecting rail wheels. In this approach, an inspector manually places the gauge on the wheel, ensures contact with all relevant portions of the wheel, reads the measurements from marked scales on the gauge, and manually enters the data. Similarly, an electronic wheel gauge can be used, which performs some of the functions automatically, thereby improving accuracy and reducing the overall time spent measuring the wheels. Various illustrative embodiments of handheld electronic wheel gauges are shown and described in U.S. Pat. No. 4,904,939, U.S. Patent Application Publication No. 2005/0259273, and U.S. Patent Application Publication No. 2007/0075192, each of which is incorporated by reference. In both approaches, the inspection is carried out by hand, on one wheel at a time, on a stationary train. To address this limitation, a number of approaches seek to measure rolling stock wheels while they are in motion, detect various defects through the measurements, and record the associated data in an automated fashion. Various illustrative embodiments of such measurement solutions are shown and described in U.S. Pat. Nos. 5,636,026, 6,768,551, 6,523,411, and U.S. Patent Application Publication No. 2007/0064244, each of which is incorporated by reference.
Frequently, rail wheels are inspected at a classification yard (e.g., hump yard, flat-shunted yard, gravity yard, and/or the like). For example, an incoming train may be halted while one or more cars are manually inspected. Often, due to time constraints, only a few cars are actually inspected and/or the inspection is only cursory (e.g., visual inspection). Subsequently, the cars on the incoming train are classified and routed to corresponding tracks for inclusion on an outgoing train. The classification is performed based on a destination for each car. Once an outgoing train is assembled, one or more cars may be manually (e.g., visually) inspected along with an inspection of the brakes for the train. Subsequently, the train will leave the classification yard for the next destination.